doc: fix/improve documentation of verdicts

doc: fix/improve documentation of verdicts

- Clarify that a terminating statement also prevents the execution of later
  statements in the same rule and give an example about that.
- Correct that `accept` won’t terminate the evaluation of the ruleset (which is
  generally used for the whole set of all chains, rules, etc.) but only that of
  the current base chain (and any regular chains called from that).
  Indicate that `accept` only accepts the packet from the current base chain’s
  point of view.
  Clarify that not only chains of a later hook could still drop the packet, but
  also ones from the same hook if they have a higher priority.
- Various other minor improvements/clarifications to wording.

Link: https://lore.kernel.org/netfilter-devel/3c7ddca7029fa04baa2402d895f3a594a6480a3a.camel@scientia.org/T/#t
Signed-off-by: Christoph Anton Mitterer <mail@christoph.anton.mitterer.name>
Signed-off-by: Florian Westphal <fw@strlen.de>